Orbital Mechanics article and applet updated

Hi folks -

I finally got a bit free time, so I rewrote the orbital mechanics
article on the Exodus Project site (http://www.ExodusProject.com) and
finally (I hope!) squashed the bug in the applet. The article is now hopefully
much easier to follow, as I've added units to all the equations throughout and
provided a summary and example for each section. The applet should be
considerably easier to use as well. I'd appreciate reports of any bugs you may
find in either item!

Thanks..